Reciprocating compressors are the most common machines available on the market. They are positive displacement compressors and can be found in ranges from fractional to very high horsepowers.
Positive displacement air compressors work by filling an air chamber with air and then reducing the chambers volume (Reciprocating, Rotary Screw and Rotary Sliding Vane are all positive displacement compressors). Reciprocating compressors work in a very similar manner as does as internal combustion engine but basically in a reverse process. They have cylinders, pistons, crankshafts, valves and housing blocks.